Page 895 - Atlas of Histology with Functional Correlations

humans, hCG appears in urine within 10 days of pregnancy, and its presence

can be used to determine pregnancy with commercial kits. hCG is similar to
luteinizing hormone in structure and function, and it maintains the corpus
luteum in the maternal ovary during the early stages of pregnancy and
stimulates it to continue producing estrogen and progesterone that are
essential for maintaining pregnancy. The placenta also secretes chorionic

somatomammotropin, a glycoprotein hormone that exhibits both lactogenic
(mammary gland stimulation) and general growth-promoting functions.

As pregnancy progresses, the placenta gradually takes over the
production of estrogen and progesterone from the corpus luteum to produce

sufficient amounts of progesterone to maintain the pregnancy until birth. The
placenta also produces relaxin, a hormone that softens the cervix and the
fibrocartilage in the pubic symphysis to widen the pelvic canal for impending
birth and placental lactogen that promotes growth and development of the

maternal mammary glands.

FIGURE 21.37 | Inactive Mammary Gland

The inactive mammary gland is characterized by connective tissue and by a

scarcity of the glandular elements. Some cyclic changes in the mammary gland
may be seen during the menstrual cycles.

A glandular lobule (1) consists of small tubules or intralobular ducts (4, 7)
lined with a cuboidal or a low columnar epithelium. At the base of the

epithelium are the contractile myoepithelial cells (6). The larger interlobular
ducts (5) surround the lobules (1) and the intralobular ducts (4, 7).

The intralobular ducts (4, 7) are surrounded by loose intralobular
connective tissue (3, 8) that contains fibroblasts, lymphocytes, plasma cells, and
eosinophils. Surrounding the lobules (1) is a dense interlobular connective

tissue (2, 10) containing blood vessels, a venule and arteriole (9).

The mammary gland consists of 15 to 25 lobes, each of which is an
individual compound tubuloalveolar gland. Each lobe is separated by dense
interlobular connective tissue. A lactiferous duct independently emerges from

each lobe at the surface of the nipple.

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